I trust Lee opinion on uha-6s mkii. He had both the O2 and the uha-6s mkii and he prefers the uha-6s mkii over the O2. It should be said that he did not try the ODAC with the O2.

I urge anyone who can to try ER4S+O2+ODAC, truly an exotic sound. The unit after 40 hours of burning in has given the Er4s the lover bass extension bass. It does not boost the bass but gives it more refinement and detail. The top end detail was great from the day one without the burn in. The sound is definitely not V-shaped but for some reason the mid-range feels less prominent than the upper and lower range.

But this combination is very transparent. I have heard so many things that I was not able to pick up with my other amp and dac combo(faint back ground vocal, singers breathing pattern, can be distracting at time but it is very fun!)

I also enjoy the HFI 780+O2+ODAC for Jazz greatly. They do a decent job on electronic.

I will try to use the ODAC+O2 with the XBA-4 and k702, fidelio M1 and SHE9900. I might buy the HD 598 and try it out but for now in summary I finally found a combination for my beloved Er4s. I can stop the search and be very happy with this combination!

I trust Lee opinion on uha-6s mkii. He had both the O2 and the uha-6s mkii and he prefers the uha-6s mkii over the O2. It should be said that he did not try the ODAC with the O2.

I urge anyone who can to try ER4S+O2+ODAC, truly an exotic sound. The unit after 40 hours of burning in has given the Er4s the lover bass extension bass. It does not boost the bass but gives it more refinement and detail. The top end detail was great from the day one without the burn in. The sound is definitely not V-shaped but for some reason the mid-range feels less prominent than the upper and lower range.

But this combination is very transparent. I have heard so many things that I was not able to pick up with my other amp and dac combo(faint back ground vocal, singers breathing pattern, can be distracting at time but it is very fun!)

I also enjoy the HFI 780+O2+ODAC for Jazz greatly. They do a decent job on electronic.

I will try to use the ODAC+O2 with the XBA-4 and k702, fidelio M1 and SHE9900. I might buy the HD 598 and try it out but for now in summary I finally found a combination for my beloved Er4s. I can stop the search and be very happy with this combination!

This is headfi and our ears are all subjected to our subjective brain, we all do not have to agree. After all what I wrote was a subjective opinion of an objective design. I guess it is not that objective after all, ehh?

PS: Have used XBA-4 for many hours now, for some odd reason my ears are not burned in yet.

LM4562 now in place in my O2. The sound is different even if the distortion measurements are identical (according to NWAVGUY) using the low gain setting. I would love to believe that the JRC 2068 is good enough - for goodness sake it is not doing much with such a low gain - but for now the LM4562 stays and the JRC2068 goes in the box with the OPA2134s

Of course, you cannot be sure of that if you made the comparison in the usual way of listening to the O2 with the NJM2068, then swapping the op amp (which takes some time, long enough to forget the finest details of the sound), and then listening to it again, knowing all the time which IC is in the amplifier.

Of course, you cannot be sure of that if you made the comparison in the usual way of listening to the O2 with the NJM2068, then swapping the op amp (which takes some time, long enough to forget the finest details of the sound), and then listening to it again, knowing all the time which IC is in the amplifier.

He needs two O2 soo , one with NJM2068 other with LM4562 , swaping the headphone plug is short enough to not be heavely biased .

I put the opamp rolling point here because I am trying to get a more listenable ODAC sound. Maybe the problem is the frequency response peak in my old Sony phones which is more apparent with the ODAC/O2. If you think that the ODAC is perfect with the standard voltage amplifier in the O2 then please consider what happens to the switching noise on the output of the ODAC. There are spikes of several mV which change polarity as the output crosses 0V. I cannot decide if this constitutes crossover distortion albeit at a pretty low level! There could be a difference in the way the voltage amplifier handles these spikes. Or this could be BS. Look I have seen the curves and as I mentioned there is no measurable difference between the recommended opamps at the low gain setting, There are some tracks where a voice or an instrument is lost in the mix but becomes apparent when I switch opamps from JRC2068 to LM4562. It is like I can read an extra line on the eyetest chart. I cannot explain it but I think the effect is real. I think the best I can do is tippex the top of my opamps then get someone else to number them. I repeat my tests to identify the opamps then scrape off the tippex to find which amps are which. If I guess 100 % correctly does that prove something?

After much amp rolling back and forth I have not come to a firm conclusion to my preference. Compared to JRC2068 , the LM4562 seems to be more detailed with better ambience and separation of the parts. On the other hand it also seems to be brighter which may be due to incorrect compensation. This may account for the apparent detail but I am not so sure that is the whole story because the separation of instruments extends into the mid and bass.

If I had some HD600s I would clearly prefer the LM4562 but as I have Sony MDR-CD570 which have significantly more treble I am not sure if I will trade the extra detail for a more balanced tone.

The ouput of the ODAC looks different today. I am using my netbook as source rather than my desktop and the output seems to be quieter. Maybe it was an earth loop between the PC and the scope picking up radiated switching transients in the ground that I saw before. Today I saw what looks like PWM which integrated down to about 5mV of high frequency sawtooth . BY the time the this noise gets through the JRC4556s in the O2 this has almost vanished.

I have to say the ODAC is still the most revealing source that I have. Unfortunately to me it sounds bright in comparison to the others (2 CD players and UCA222)

I've tried whatever OPAMPs I've had that would fit (some are singles and a Browndog DIP adaptor is too big). The feel the differences between them are very minor. My attitude is that I'll just leave whatever I have spare in there, though I'll probably drop the NE5532 back in it if I decide to review any headphones for consistency (I can't get the JRC2068 from Mouser here and haven't gotten around to sourcing it locally). At some point I will grab an ODAC out of curiosity, but also to have a basic reference system that a large number of people are famliar with when I write impressions of headphones.